Cryogenic Technology Development for Exploration Missions

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David J. Chato. Glenn Research Center, Cleveland, Ohio. Cryogenic Technology Development for Exploration Missions. NASA/TM—2007-214824. September ...

NASA/TM—2007-214824

Cryogenic Technology Development for Exploration Missions David J. Chato Glenn Research Center, Cleveland, Ohio

September 2007

AIAA–2007–0953

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NASA/TM—2007-214824

Cryogenic Technology Development for Exploration Missions David J. Chato Glenn Research Center, Cleveland, Ohio

Prepared for the 45th AIAA Aerospace Sciences Meeting and Exhibit sponsored by the American Institute of Aeronautics and Astronautics Reno, Nevada, January 8–11, 2007

National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135

September 2007

AIAA–2007–0953

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Cryogenic Technology Development for Exploration Missions David J. Chato National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135

Abstract This paper reports the status and findings of different cryogenic technology research projects in support of the President’s Vision for Space Exploration. The exploration systems architecture study is reviewed for cryogenic fluid management needs. It is shown that the exploration architecture is reliant on the cryogenic propellants of liquid hydrogen, liquid oxygen and liquid methane. Needs identified include: the key technologies of liquid acquisition devices, passive thermal and pressure control, low gravity mass gauging, prototype pressure vessel demonstration, active thermal control; as well as feed system testing, and Cryogenic Fluid Management integrated system demonstration. Then five NASA technology projects are reviewed to show how these needs are being addressed by technology research. Projects reviewed include: In-Space Cryogenic Propellant Depot; Experimentation for the Maturation of Deep Space Cryogenic Refueling Technology; Cryogenic Propellant Operations Demonstrator; Zero Boil-Off Technology Experiment; and Propulsion and Cryogenic Advanced Development. Advances are found in the areas of liquid acquisition of liquid oxygen, mass gauging of liquid oxygen via radio frequency techniques, computational modeling of thermal and pressure control, broad area cooling thermal control strategies, flight experiments for resolving low gravity issues of cryogenic fluid management. Promising results are also seen for Joule-Thomson pressure control devices in liquid oxygen and liquid methane and liquid acquisition of methane, although these findings are still preliminary.

I.

Introduction

The President’s Vision for Space Exploration (VSE) (ref. 1) articulated a need for future space technologies. One of its goals is to develop the innovative technologies, knowledge, and infrastructures both to explore and to support decisions about the destinations for human exploration. It is the author’s belief that one of the technologies that will be key is Cryogenic Fluid Management (CFM). The Vision for Space Exploration also identifies in its goals developing and demonstrating propulsion systems required to support more distant, more capable, and longer duration human and robotic exploration. Achieving this goal will require many cryogenic propulsion system elements that need to operate in Low Earth Orbit (LEO) and lunar orbits for long periods, as well as during transit to Mars or other destinations. CFM technology is essential to implementing the propulsion systems required for carrying out future exploration missions. For cryogenic propellants (oxygen, hydrogen, and methane), the technology needed for future long duration missions has yet to be demonstrated in space. Future exploration missions can be greatly enhanced with the development of a robust, space or extraterrestrial based cryogenic fluid management, storage and distribution system. Extended presence of humans on the Moon and the exploration of Mars will depend on the long term storage and efficient use of cryogenic fluids for life support gases and high energy propellants. Developing a robust cryogenic fluid management system will allow humans to safely travel to and work on the Moon and Mars for extended periods. Storage of these fluids as a sub-critical liquid enables lightweight propellant tanks and distribution components. This then reduces the earth launch mass requirements for these components allowing more launch payload mass for critical scientific experiments. The basic CFM elements and functions of such a system include: storage, pressure control, fluid transfer, liquid acquisition fluid couplings, instrumentation, leak detection and quantity gauging. A combination of passive and active thermal control (refrigeration) could allow cryogenic propellants to be stored indefinitely with no losses, i.e., with zero boil-off (ZBO). A ZBO approach may be vital to missions requiring storage of propellants for durations of six months or more. Cryogenic propellant transfer operations allow the reuse of hardware already in orbit, thus reducing lift mass. Stages filled on-orbit can eliminate many of the crewed launch vehicle and structural mass and systems required to support and maintain cryogens on the launch pad.

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In response to this need NASA initiated several research programs to advance the state-of-the-art in CFM technology. This paper will report the current status and findings of these efforts. In the first part of the paper we will review the Exploration Systems Architecture Study (ref. 2) (ESAS) and their use of CFM technologies. In the second part of the paper we will discuss the results of technology efforts to date. These include the “In-Space Cryogenic Propellant Depot (ISCPD),” “Experimentation for the Maturation of Deep Space Cryogenic Refueling Technology (MDSCR)” including the follow-on “Cryogenic Propellant Operations Demonstrator” (CPOD) and the Zero Boil–Off Tank (ZBOT) flight experiments. All of these except for CPOD were initiated prior to the ESAS. The ISCPD and MDSCR projects have since been brought to a close. Although CPOD was not selected for the flight opportunity for which it was proposed the research team continues to advocate its benefit to the future exploration vehicle development and to review potential flight opportunities as they become available. The ZBOT experiment which has received some development funding continues although it has been decoupled from near term ESAS goals. Subsequent to the ISCPD and MDSCR projects the Propulsion and Cryogenic Advanced Development Project (PCAD) was initiated to support advanced development of CFM technology for the cryogenic propellant combinations recommended by the ESAS report. It is the intent of this paper to show the continuity of CFM technology research between these projects.

II. Architecture Study Cryogenic propellant combinations are found throughout the baseline ESAS. Although several propellant changes have been proposed to the ESAS architecture since its release in December 2005 the cryogenic propellant combinations remain under discussion, so the baseline will be used as a representative example. The Crew Exploration Vehicle (CEV) serves as the primary human transport of ESAS. ESAS sized the CEV for the human lunar return and used deltas to size the International Space Station (ISS) crew mission and Mars mission versions. The CEV command module is an Apollo like capsule which has no cryogens. Its propulsion is limited to Reaction Control Systems (RCS) only. The cryogenic propellant version of the CEV service module contains liquid oxygen and liquid methane. A pressure fed main engine provides propulsion for; rendezvous and docking with the lunar access module in earth orbit; contingency plane changes prior to lunar ascent; trans-earth injection; and self disposal. RCS thrusters provide on-orbit maneuvering. All thrusters are fed propellants from common tank sets of oxygen and methane. Helium pressurant bottles maintain the tank pressure. These bottles are thermally coupled to the methane tank to reduce the volume of the gaseous helium. Cryogenic fluid management systems for the CEV service module include passive storage multilayer insulation blankets for thermal control and thermodynamic vent systems for tank pressure control. Also, use of common propellant storage tanks for main engine and RCS engines will require a cryogenic liquid acquisition device (LAD) capable of feeding RCS thrusters in low gravity. Some of the later exploration missions may require stays at the ISS as long as six months possibly requiring augmentation of the passive storage systems with active refrigeration. Although the first stage of the Crew Launch Vehicle (CLV) is a non-cryogenic solid rocket booster, it requires a large cryogenic upper stage to complete its mission. The baseline design uses a Space Shuttle Main Engine (SSME) and uses liquid oxygen and liquid hydrogen as its propellants. Cryogenic fluid management systems for this stage are similar to those used on current launch vehicles. The Cargo Launch Vehicle (CaLV) uses a cryogenic liquid hydrogen-oxygen first stage core and upper earth departure stage of liquid hydrogen and liquid oxygen. The large mass and thrust of the CaLV mandate the use of high performance cryogenic propellants. Cryogenic systems for the first stage core are similar to the existing shuttle systems. The Earth Departure Stage (EDS) is another story. Approximately 60 percent of the EDS propellant is consumed in achieving a stable orbit. The remaining 40 percent must be stored until the CEV can be launched and rendezvous with the orbiting EDS. The EDS is restarted to propel the coupled CEV into lunar transit. The baseline study estimated the rendezvous time as a few weeks, but more recent analysis has suggested an even longer time of 95 days. Although Expendable Launch Vehicle (ELV) upper stages have demonstrated coasts as long as 9 hr, the EDS coast duration is several orders of magnitude beyond. Clearly using the boil-off venting to settle propellants as the Saturn rocket did is not viable for such an extended on-orbit time. The Lunar Surface Access Module (LSAM) is a two stage vehicle, one stage for descent to the lunar surface and one stage for ascent from there. The LSAM ascent stage is similar to the CEV in being liquid oxygen/methane fueled, while the LSAM descent stage will be liquid oxygen/hydrogen like the EDS. The

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LSAM ascent stage’s location near the end of the mission means that every kilogram saved here results in many kilograms saved on the CaLV weight. This makes the light weight of cryogenic propellants very attractive. CFM issues are similar to EDS except that the LSAM must wait with the EDS until the CEV arrives. This will increase the storage time required over that of CEV. In fact some of the later lunar base missions may require 6 months of storage (similar to the CEV at ISS) for the LSAM ascent stage. In the technology assessment portion of the ESAS report the following cryogenic fluid management technologies were considered key: Liquid acquisition devices, passive thermal and pressure control, low gravity mass gauging, prototype pressure vessel demonstration, active thermal control, and CFM integrated system demonstration. It was also felt that RCS feed system testing with liquid oxygen and liquid methane would prove important.

III. Technology Projects A. In-Space Cryogenic Propellant Depot The In-Space Cryogenic Propellant Depot (ISCPD) project was designed to develop the technology required to manage and store large quantities of cryogenic propellants on-orbit. The ISCPD project encompassed a broad range of activities including architecture studies, CFD modeling, and ground testing of components and integrated systems. Components to be investigated included LADs, mass gauges, miniature leak detectors, cryocoolers, fluid umbilicals and fluid connectors. The goals of the ISCPD project are documented in Howell (ref. 3). Howell calls for CFM research in the area of liquid acquisition to develop a database for capillary screen wicking characteristics, surface tension data, and screen outflow performance to enable a depot capable of providing vapor free liquid down to a 2 percent residual level. He recommends development of a mass gauge with accuracy better than 5 percent. ISCPD mass gauging research and development has included work on optical, compression, and radio frequency gauges with the concept of down selecting to a best approach based on test results and systems analysis. Minimal or zeroloss (i.e., zero boil-off) cryogenic storage is required with goal of

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